Cardiac muscle cell formation after development of the linear heart tube.

After the development of the linear heart tube, additional myocardium is formed leading to the muscular mantle around the caval and pulmonary veins and the muscular septa in the embryonic heart. Here, we report the results of our in vivo and in vitro studies of this late myocardium-generating process in the mouse. By using an immunohistochemical approach, we determined that myocardium formation starts around embryonic day 12 in the dorsal mesocardium. In subsequent stages of development, the process extends downstream into the intracardiac mesenchymal tissues of the atrioventricular canal and outflow tract and upstream into the extracardiac mediastinal mesenchyme embedding the pulmonary and caval veins. Given the spatiotemporal pattern of myocardium formation, we applied a three-dimensional in vitro explant culture assay to investigate the myocardium-generating potential of the different cardiac compartments. We determined that this potential is stage- and mesenchyme-dependent. This latter finding suggests an important role for mesenchyme in myocardium formation after the development of the linear heart tube.     

Breakthroughs in molecular and cellular mechanisms underlying X-linked mental retardation.

Although genetic causes of X-linked mental retardation (XLMR) are heterogeneous and complex, recent concerted actions between physicians and biologists have allowed some major difficulties to be overcome and led to the identification of an increasing number of genes involved in these conditions. Indeed, over the past 2 years significant progress has been made in understanding the molecular basis underlying not only XLMR, where there are distinguishing phenotypic or genetic markers (syndromal forms of XLMR), but also non-specific (or idiopathic) mental retardation (MRX). Recent breakthroughs have shown that genes responsible for these latter conditions encode for proteins involved in signalling pathways which regulate cytoskeleton organization, synaptic vesicle transport and, maybe, other cellular functions. Also, they suggest a provacative picture that conceptualizes MRX as disorders resulting from a dysfunctioning of genes required for processes such as the remodelling, establishment and stabilization of connections between neuronal cells. Such processes are crucial for the development of intellectual and cognitive functions. As these functions begin to evolve mainly in post-natal stages through contact with diverse stimuli and environments, a potential therapeutic approach would be the development of drugs that target cellular signalling pathways shown to be implicated in MRX.     

Temporospatial distribution of matrix metalloproteinase and tissue inhibitors of matrix metalloproteinases during murine secondary palate morphogenesis

Extracellular matrix (ECM) molecules are known to play a pivotal role in the morphogenesis of the secondary palate. The maintenance and degradation of the ECM is mediated in part by the matrix metalloproteinases (MMPs) and their endogenous inhibitors TIMPs. MMPs and TIMPs have previously been shown to be developmentally regulated within the palatal shelf during secondary palate morphogenesis. This study was conducted to examine the temporospatial distribution of these enzymes and their inhibitors within the palatal shelves using immunofluorescent localization to determine if specific changes occur in their distribution concomitant with events in palatal shelf formation and reorientation. Frontal sections through the posterior palatal shelves at gestational day (gd) 12, 13 and 14 were immunofluorescently stained for MMPs 2, 3, 9, and 13 and TIMPs 1, 2, and 3 using standard protocols and commercially available antibodies. The results demonstrated that MMPs and TIMPs were already present within the palatal shelf mesenchyme 30 h prior to reorientation and closure and that their expression within the shelf mesenchyme increased as the shelves remodeled, then decreased with closure and fusion. Increased distribution of MMPs and TIMPs within specific regions of the palatal mesenchyme and palatal epithelial basement membrane preceded decreases previously observed within these areas for their substrates, fibronectin, collagen III and collagen I. In addition, MMP-3 and TIMP-3 were immunolocalized to regions of the palatal epithelium that undergo reorganization concomitant with reorientation. The results of this study indicate that MMPs and TIMPs are developmentally regulated during palatal shelf morphogenesis and that their distribution correlates with the distribution of the ECM components of the palatal shelf they regulate. These results provide support for the idea that temporospatially controlled interactions between MMPs and their substrates may be pivotal in modulating events in palatal morphogenesis. Accepted: 3 March 2000     

Cardiac looping in experimental conditions: effects of extraembryonic forces.

The chick embryo is a popular experimental model used to study the mechanisms of cardiac looping. To facilitate oxygen transport, researchers typically culture the embryo on the surface of the medium. Such preparations, however, expose the embryo and the heart to surface tension that is not present in ovo. This study investigates the influence that surface and extraembryonic membrane tensions have on looping morphology. To eliminate surface tension, we developed a technique in which the embryo is cultured under a thin layer of fluid. To eliminate membrane tension, the membrane was removed. Our results show that both tensions can affect looping, with surface tension potentially having a much greater effect. Moreover, we show that surface tension can alter results in one classic looping experiment.     

Cellular mechanisms of neural fold formation and morphogenesis in the chick embryo

The mechanisms underlying neural fold formation and morphogenesis are complex, and how these processes occur is not well understood. Although both intrinsic forces (i.e., generated by the neuroepithelium) and extrinsic forces (i.e., generated by non-neuroepithelial tissues) are known to be important in these processes, the series of events that occur at the neural ectoderm-epidermal ectoderm (NE-EE) transition zone, resulting in the formation of two epithelial layers from one, have not been fully elucidated. Moreover, the region-specific differences that exist in neural fold formation and morphogenesis along the rostrocaudal extent of the neuraxis have not been systematically characterized. In this study, we map the rostrocaudal movements of cells that contribute to the neural folds at three distinct brain and spinal cord levels by following groups of dye-labeled cells over time. In addition, we examine the morphology of the neural folds at the NE-EE transition zone at closely-spaced temporal intervals for comparable populations of neural-fold cells at each of the three levels. Finally, we track the lateral-to-medial displacements that occur in the epidermal ectoderm during neural groove closure. The results demonstrate that neural fold formation and morphogenesis consist of a series of processes comprising convergent-extension movements, as well as epithelial ridging, kinking, delamination, and apposition at the NE-EE transition zone. Regional differences along the length of the neuraxis in the respective roles of these processes are described.     

Molecular and cellular mechanisms underlying anti-neuronal antibody mediated disorders of the central nervous system

Over the last decade multiple autoantigens located on the plasma membrane of neurons have been identified. Neuronal surface antigens include molecules directly involved in neurotransmission and excitability. Binding of the antibody to the antigen may directly alter the target protein's function, resulting in neurological disorders. The often striking reversibility of symptoms following early aggressive immunotherapy supports a pathogenic role for autoantibodies to neuronal surface antigens. In order to better understand and treat these neurologic disorders it is important to gain insight in the underlying mechanisms of antibody pathogenicity. In this review we discuss the clinical, circumstantial, in vitro and in vivo evidence for neuronal surface antibody pathogenicity and the possible underlying cellular and molecular mechanisms. This review shows that antibodies to neuronal surface antigens are often directed at conformational epitopes located in the extracellular domain of the antigen. The conformation of the epitope can be affected by specific posttranslational modifications. This may explain the distinct clinical phenotypes that are seen in patients with antibodies to antigens that are expressed throughout the brain. Furthermore, it is likely that there is a heterogeneous antibody population, consisting of different IgG subtypes and directed at multiple epitopes located in an immunogenic region. Binding of these antibodies may result in different pathophysiological mechanisms occurring in the same patient, together contributing to the clinical syndrome. Unraveling the predominant mechanism in each distinct antigen could provide clues for therapeutic interventions.     

基质金属蛋白酶及其抑制剂在腹主动脉瘤发病中的作用

随着现代医学的发展 ,腹主动脉瘤 (ａｂｄｏｍｉｎａｌａｏｒｔｉｃａｎｅｕｒｙｓｍｓ ,ＡＡＡ)在临床上已得到有效治疗 ,但本病的促发因素以及持续扩张以致破裂的控制因素仍存在较大的争议 ,经过免疫、遗传、分子生物学及血流动力学等方面的广泛研究 ,所有学者均认为腹主动脉壁的基质降解是ＡＡＡ形成和发展的关键环节 ,基质金属蛋白酶 (ｍａｔｒｉｘｍｅｔａｌｌｏｐｒｏｔｅｉｎａｓｅ ,ＭＭＰ)是破坏细胞外基质 (ｅｘｔｒａｃｅｌｌｕｌａｒｍａｔｒｉｘ ,ＥＣＭ )中最主要一类酶系 ,本文就ＭＭＰ及其抑制剂类别功能、来源与表达以及两…     

染料木黄酮的抗巨噬细胞泡沫化效应及其分子机制研究

目的 研究染料木黄酮对动脉粥样硬化过程中巨噬细胞泡沫化的抑制作用,并探讨其抗泡沫化的分子作用机制.方法 采用体外ox-LDL诱导小鼠单核巨噬细胞RAW264.7产生泡沫化,通过油红O染色观察细胞内脂质聚集程度判定细胞的泡沫化程度以及药物效应;利用报告基因细胞检测方法评价染料木黄酮对代谢性核受体过氧化物酶体增殖物激活受体PPAR和肝X受体LXR的转录调控功能的激动作用;利用实时定量PCR检测染料木黄酮对巨噬细胞中ox-LDL摄取以及胆固醇逆转运相关基因的mRNA水平.结果 ox-LDL处理的空白组小鼠RAW264.7单核巨噬细胞内聚积大量的脂质,而经过10 ug/ml染料木黄酮处理后的RAW264.7细胞内脂滴量明显减少,细胞泡沫化程度被大幅度降低.瞬时转染的细胞报告基因的转录激活效应研究结果说明,染料木黄酮对核受体PPAR和LXR均有较高的转录激活效应,其EC50值分别为3.5～9.2 μg/ml和1.6 ～ 3.3 μg/ml.定量PCR研究结果显示,染料木黄酮可以有效地使巨噬细胞中的胆固醇逆转运基因LXRα、LXRβ、ABCA1、ABCGl、和SR-B1的表达上调,而作为主要摄取ox-LDL受体的CD36基因的表达无明显变化.结论 染料木黄酮可以有效抑制动脉粥样硬化过程中巨噬细胞的泡沫化,而该作用机制可能是通过激活PPAR和LXR通路,上调胆固醇逆转运蛋白的ABCA1、ABCG1、LXRα、LXRβ、SR-B1基因的表达,增强了巨噬细胞的胆固醇外排,从而防止动脉粥样硬化的发生和发展.     

Prognostic significance of matrix metalloproteinase 2 and tissue inhibitor of metalloproteinase 2 expression in prostate cancer.

Matrix metalloproteinases (MMPs) are proteolytic enzymes capable of degrading the structural support network for normal and malignant cells, promoting neoplastic cell invasion and metastasis. Tissue inhibitors of metalloproteinases (TIMPs) maintain connective tissue integrity by modulating MMP activity. Formalin-fixed paraffin-embedded tissue sections from 138 prostatic adenocarcinomas (PACs) were immunostained by a combined automated/manual method using monoclonal antibodies against MMP2 and TIMP2. Immunoreactivity was semiquantitatively scored based on stain intensity and distribution, and results were correlated with Gleason grade, pathologic stage, ploidy status, and disease recurrence. One hundred five of 138 (76%) and 113/138 (82%) PACs expressed MMP2 and TIMP2, respectively. Co-expression was observed in 94/138 (68%) of PACs (P =.01), correlated with advanced tumor stage (P =.05), and tended to be associated with disease recurrent cases (P =.07). TIMP2 expression individually correlated with advanced tumor stage (P =.04) and reached near significance with disease recurrence (P =.06). MMP2 expression was also more frequent in recurrent PACs, although this value did not reach statistical significance (P =.07). However, on multivariate analysis, only pathologic stage (P =.009) and ploidy status (P =.03) independently predicted disease recurrence. In conclusion, MMP2 and TIMP2 are co-expressed in a majority of PACs and correlate with prognostic variables. Interestingly, contrary to the previously documented anti-tumor effects of TIMPs, TIMP2 expression appears to have a tumor-promoting role in PACs and warrants further investigation.     

Differential expression of matrix metalloproteinase and tissue inhibitor of matrix metalloproteinase genes in the mouse central nervous system in normal and inflammatory states.

Matrix metalloproteinases (MMPs) are implicated in the pathogenesis of inflammatory disorders of the central nervous system (CNS) whereas the contribution of the major endogenous counter-regulators of MMPs, the tissue inhibitors of the matrix metalloproteinases (TIMPs), is unclear. We investigated the temporal and spatial expression patterns in the CNS of nine MMP genes and three TIMP genes in normal mice, in mice with EAE, and in transgenic mice with astrocyte (glial fibrillary acidic protein)-targeted expression of the cytokines interleukin-3 (macrophage/microglial demyelinating disease), interleukin-6 (neurodegenerative disease), or tumor necrosis factor-alpha (lymphocytic encephalomyelitis). In normal mice, the MMPs MT1-MMP, stromelysin 3, and gelatinase B were expressed at low levels, whereas high expression of TIMP-2 and TIMP-3 was observed predominantly in neurons and in the choroid plexus, respectively. In EAE and the transgenic mice, significant induction or up-regulation of various MMP genes was observed, the pattern of which was somewhat specific for each of the models, and there was significant induction of TIMP-1. In situ localization experiments revealed a dichotomy between MMP expression that was restricted to leukocytes and possibly microglia within inflammatory lesions and TIMP-1 expression that was observed in activated astrocytes circumscribing the lesions. These findings demonstrate specific spatial and temporal regulation in the expression of individual MMP and TIMP genes in the CNS in normal and inflammatory states. The distinct localization of TIMP-1 and MMP expression during CNS inflammation suggests a dynamic state in which the interplay between these gene products may determine both the size and resolution of the destructive inflammatory focus.     

Cardiac looping in the chick embryo: a morphological review with special reference to terminological and biomechanical aspects of the looping process

Understanding early cardiac morphogenesis, especially the process of cardiac looping, is of fundamental interest for diverse biomedical disciplines. During the past few years, remarkable progress has been made in identifying molecular signaling cascades involved in the control of cardiac looping. Given the rapid accumulation of new data on genetic, molecular, and cellular aspects of early cardiac morphogenesis, and given the widespread interest in cardiac looping, it seems worth reviewing those aspects of the looping process that have received less attention during the past few years. These are terminological problems, the "gross" morphological aspects, and the biomechanical concepts of cardiac looping. With respect to terminology, emphasis is given to the unperceived fact that different viewpoints exist as to which part of the normal sequence of morphogenetic events should be called cardiac looping. In a short-term version, which is preferred by developmental biologists, cardiac looping is also called dextral- or rightward-looping. Dextral-looping comprises only those morphogenetic events leading to the transformation of the originally straight heart tube into a c-shaped loop, whose convexity is normally directed toward the right of the body. Cardioembryologists, however, regard cardiac looping merely as a long-term process that may continue until the subdivisions of the heart tube and vessel primordia have approximately reached their definitive topographical relationship to each other. Among cardioembryologists, therefore, three other definitions are used. Taking into account the existence of four different definitions of the term cardiac looping will prevent some confusion in communications on early cardiac morphogenesis. With respect to the gross morphological aspects, emphasis is given to the following points. First, the straight heart tube does not consist of all future regions of the mature heart but only of the primordia of the apical trabeculated regions of the future right and left ventricles, and possibly a part of the primitive conus (outflow tract). The remaining part of the primitive conus and the primordia of the great arteries (truncus arteriosus), the inflow of both ventricles, the primitive atria, and the sinus venosus only appear during looping at the arterial (truncus arteriosus) and venous pole (other primordia). Second, dextral-looping is not simply a bending of the straight heart tube toward the right of the body, as it has frequently been misinterpreted. It results from three different morphogenetic events: (a) bending of the primitive ventricular region of the straight heart tube toward its original ventral side; (b) rotation or torsion of the bending ventricular region around a craniocaudal axis to the right of the body, so that the original ventral side of the heart tube finally forms the right convex curvature and the original dorsal side forms the left concave curvature of the c-shaped heart loop; (c) displacement of the primitive conus to the right of the body by kinking with respect to the arterial pole. Third, dextral-looping does not bring the subdivisions of the heart tube and vessel primordia approximately into their definitive topographical relationship to each other. This is achieved by the morphogenetic events following dextral-looping. This review seeks to bring together data from the diverse disciplines working on the developing heart.     

Circuit mechanisms underlying memory encoding and retrieval in the long axis of the hippocampal formation

Circuits within the hippocampal formation are active during memory processing. Here we used functional magnetic resonance imaging (fMRI) to examine multiple sites across the long axis of the hippocampal formation while subjects performed different phases of an associative memory task, learning to associate faces with names. Viewing faces and hearing names in isolation resulted in separate hippocampal activation patterns. Pairing faces with names resulted a spatially redistributed activation pattern, rather than a simple summation of the activation patterns resulting from viewing faces and hearing names in isolation. Recalling names when cued with faces reactivated a pattern similar to that found during paired training. Finally, the activation patterns representing faces and names were found to be experience dependent, emerging with repeated exposure. Interpreted in the context of hippocampal anatomy and physiology, these findings reveal hippocampal circuit mechanisms that underlie memory encoding and retrieval.     

Dynamic interactions between the cellular components of the heart and the extracellular matrix

The heart is composed of both cellular and acellular components that act in a dynamic fashion from birth to death. The cellular components consist of myocytes, fibroblasts, and vascular cells, including endothelium and smooth muscle. Changes in these components are intimately associated with function by altering the mechanical, chemical, and electrical properties of the heart. In future investigations, it will be important to examine these interactions as dynamic changes in response to physiological signals.     

Membrane-type-1 matrix metalloproteinase, matrix metalloproteinase 2, and tissue inhibitor of matrix proteinase 2 in prostate cancer: identification of patients with poor prognosis by immunohistochemistry

Overexpression of the matrix metalloproteinase (MMP) 2 is associated with poor prognosis in many tumor types. Membrane-type-1 MMP (MMP14) activates MMP2 using pro-MMP2 specific inhibitor, tissue inhibitor of matrix proteinase 2 (TIMP2), as a receptor. We evaluated, by immunohistochemistry on 189 T3N0-2M0 prostate cancer (Pca) cases, the influence of MMP2, MMP14, and TIMP2 expression, individually and in association, on Pca disease-free survival (DFS). We evaluated marker expression separately in cancer, stromal, and benign epithelial (BE) cells according to a percentage scale (0%, <10%, 10%-50%, and >50%). Median follow-up was 4.61 years. In BE cells, there was an inverse relationship between initial prostate-specific antigen serum level and T3 stage with MMP14 expression (P = .003) and between pN stage and TIMP2 expression (P = .04). The most significant results with survival were obtained by dichotomizing the cases between those with less than 10% and at least 10% of cells expressing the marker, the latter category representing overexpression. TIMP2 overexpression in stromal cells was associated with a longer DFS with a hazard ratio of 0.573 (P = .02) for time to recurrence. MMP2 overexpression by BE cells correlated with a shorter DFS using a multivariate trend test (hazard ratio = 1.46, P = .02). Stromal cells expressing less than 10% TIMP2 and MMP2 overexpression was the only combination that was significantly associated with a shorter DFS (log-rank test, P = .0001). This study suggests that MMP14 is involved mostly in Pca implantation and that MMP2 and TIMP2 expression by reactive stromal cells might be used as predictors of DFS in T3N0-2M0 Pca.     

Control of hepatocyte function on collagen foams: sizing matrix pores toward selective induction of 2-D and 3-D cellular morphogenesis

While microporous biopolymer matrices are being widely tested as cell culture substrates in hepatic tissue engineering, the microstructural basis for their control of cell differentiation is not well understood. In this paper, we studied the role of void size of collagen foams in directing the induction of liver-specific differentiated morphology and secretory activities of cultured rat hepatocytes. Hepatocytes cultured on collagen foams with subcellular sized pore diameters of 10 microm assumed a compact, cuboidal cell morphology, rapidly achieving monolayer coverage, and secreted albumin at the rate of 40 +/- 8 pg/cell/d. Increasing the pore size to 18 microm elicited a distinctly spread cellular phenotype, with discontinuous surface coverage, and albumin secretion rates declined precipitiously to 3.6 +/- 0.8 pg/cell/d. However, when collagen foams with an even higher average void size of 82 microm were used, hepatocytes exhibited high degree of spreading within an extensive three-dimensional cellular network, and exhibited high albumin secretory activity (26 +/- 0.6 pg/cell/d). The effect of void geometry on cellular ultrastructral polarity was further analyzed for the three void size configurations employed. The distribution of the cell-cell adhesion protein, E-cadherin, was primarily restricted to cell-cell contacts on the 10 microm foams, but was found to be depolarized to all membrane regions in cells cultured on the 18 and 82 microm foams. Vinculin-enriched focal adhesions were found to be peripherally clustered on cells cultured on 10 microm foams, but were found to redistribute to the entire ventral surface of cells cultured on the 18 and 82 microm foams. Overall, we demonstrate the significance of designing pore sizes of highly adhesive substrates like collagen toward selective cell morphogenesis in 2-D or 3-D. Subcellular and supercellular ranges of pore size promote hepatocellular differentiation by limiting 2-D cell spreading or effecting 3-D intercellular contacts, while intermediate range of pore sizes repress differentiation by promoting 2-D cell spreading.